Part 1 of 3

Code E026 - Quad-Driver (QDM) Circuit (Part 1 of 3):

Wiring Diagram for Code E026 - Quad-Driver (QDM) Circuit:

CIRCUIT DESCRIPTION:

The ECM is used to control several components such as those illustrated above. The ECM controls these devices through the use of a quad-driver module (QDM). When the ECM is commanding a component "ON," the voltage potential of the output circuit will be "low" (near 0 volt). When the ECM is commanding the output circuit to a component "OFF," the voltage potential of the circuit will be "high." (Near battery voltage.) The primary function of the QDM is to supply the ground for the component being controlled. Each QDM has a fault line which is monitored by the ECM.

The fault line signal is available on the data stream for "Scan" tool test equipment. The ECM will compare the voltage at the QDM based on accepted values of the fault line. If the QDM fault detection circuit senses a voltage other than the accepted value, the fault line will go from a "low" signal on the data stream to a "high" signal and a code 26 will set if applicable. Some QDM circuits will switch from "low" to "high" normally.

Examples: QDM 2 - If A/C pressure switch closes and turns "ON" high speed coolant fan or QDM 3 - If the brake is depressed. These conditions are normal and no code 26 is set. These are accepted conditions. A fault on QDM 2 will not set a code 26, diagnosis may be done by making sure the A/C is turned "OFF".

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. The ECM does not know which controlled circuit caused the code E026 so this chart will go through each of the circuits to determine which is at fault. This test checks the "Service Engine Soon" light driver and the "SERVICE ENGINE SOON" light circuit.

2. QDM Symptoms:
- TCC - Inoperative - Code E039.
- EGR - Inoperative - Codes E063, E064, E065.
- Coolant fan on low speed all the time or won't come on at all.
- Poor driveability due to 100% canister purge.